From Mike Harrington of The Sabres Edge (Buffalo News) blog,

Buffalo Sabres coach Lindy Ruff left practice early today in First Niagara Center after taking a scary fall in the wake of a collision with defenseman Jordan Leopold.

Leopold was working in a 1-on-1 drill with Ville Leino and lost his balance, sliding to the ice and barreling into Ruff from behind. Ruff went airbone and landed hard on the ice, letting out a scream as his body crumpled that echoed through the empty arena.